Water soluble paa-based polymer blends as binders for si dominant anodes

ABSTRACT

Systems and methods utilizing water soluble (aqueous) PAA-based polymer binders for silicon-dominant anodes may include an electrode coating layer on a current collector, where the electrode coating layer is formed from silicon and a pyrolyzed water soluble PAA-based polymer blend, wherein the water soluble PAA-based polymer blend comprises PAA and one or more additional water-soluble polymer components. The electrode coating layer may include more than 70% silicon and the anode may be in a lithium ion battery.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application is a continuation of and claims the benefit of U.S.application Ser. No. 17/344,726 filed Jun. 10, 2021, pending (nowallowed). The entirety of the above referenced application is herebyincorporated by reference.

FIELD

Aspects of the present disclosure relate to energy generation andstorage. More specifically, certain embodiments of the disclosure relateto a method and system for water soluble (aqueous) PAA-based polymerbinders for silicon-dominant anodes.

BACKGROUND

Conventional approaches for battery electrodes may be costly,cumbersome, and/or inefficient—e.g., they may be complex and/or timeconsuming to implement, and may limit battery lifetime.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present disclosureas set forth in the remainder of the present application with referenceto the drawings.

BRIEF SUMMARY

A system and/or method for using water soluble PAA-based polymer bindersfor silicon anodes in Li-ion battery electrodes, substantially as shownin and/or described in connection with at least one of the figures, asset forth more completely in the claims.

These and other advantages, aspects and novel features of the presentdisclosure, as well as details of an illustrated embodiment thereof,will be more fully understood from the following description anddrawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a battery, in accordance with an exampleembodiment of the disclosure.

FIG. 2 illustrates the two step interaction of PAA with phenolic resinsto form a polymeric blend, which is then used as a binder, and thefurther carbonization step to create the conductive matrix, inaccordance with an example embodiment of the disclosure.

FIG. 3A is a flow diagram of a direct coating process for fabricating acell with a silicon-dominant electrode, in accordance with an exampleembodiment of the disclosure.

FIG. 3B is a flow diagram of an alternative process for lamination ofelectrodes, in accordance with an example embodiment of the disclosure.

FIG. 4 illustrates roll-to-roll coating of Si dominant anodes usingaqueous based PAA-phenolic resin polymer blend and water (as thesolvent), in accordance with an example embodiment of the disclosure.

FIG. 5 shows SEM images of the Si anode before (a, c) and afterpyrolyzation (c, d), in accordance with an example embodiment of thedisclosure. The as-coated Si anode is denoted as “green anode”.

FIG. 6 is a plot comparing the nominal capacity retention of anodesprepared using a water soluble PAA-based polymer binder versus astandard anode prepared using organic solvent, in accordance with anexample embodiment of the disclosure. The onset image shows a digitalphotograph of the final pyrolyzed Si anodes prepared using PAA-phenolicresin binder and water (solvent).

FIG. 7 shows TGA data illustrating the char yield of a phenol-PAApolymer blend, in accordance with an example embodiment of thedisclosure.

FIG. 8 is a plot comparing the coulombic efficiency of anodes preparedusing a water soluble PAA-based polymer binder versus a standard anodeprepared using organic solvent, in accordance with an example embodimentof the disclosure.

FIG. 9 shows the normalized capacity retention for aqueous based anodesprepared using phenolic-PAA with a 1:3.67 wt/wt ratio as the binder inSi anode as compared to anodes prepared using phenolic-PAA with a 1:2.45wt/wt ratio, in accordance with an example embodiment of the disclosure.

FIG. 10 shows internal resistance for 60 s pulses during charge foraqueous based anodes prepared using phenolic-PAA with a 1:3.67 wt/wtratio as the binder in Si anode as compared to anodes prepared usingphenolic-PAA with a 1:2.45 wt/wt ratio, in accordance with an exampleembodiment of the disclosure.

FIG. 11 shows 2C cycling data for aqueous based anodes prepared usingphenolic-PAA+Al30 vs. NMP based anode, in accordance with an exampleembodiment of the disclosure.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a battery with silicon-dominant anodes, inaccordance with an example embodiment of the disclosure. Referring toFIG. 1 , there is shown a battery 100 comprising a separator 103sandwiched between an anode 101 and a cathode 105, with currentcollectors 107A and 107B. There is also shown a load 109 coupled to thebattery 100 illustrating instances when the battery 100 is in dischargemode. In this disclosure, the term “battery” may be used to indicate asingle electrochemical cell, a plurality of electrochemical cells formedinto a module, and/or a plurality of modules formed into a pack.Furthermore, the cell shown in FIG. 1 is a very simplified examplemerely to show the principle of operation of a lithium ion cell.Examples of realistic structures are shown to the right in FIG. 1 ,where stacks of electrodes and separators are utilized, with electrodecoatings typically on both sides of the current collectors. The stacksmay be formed into different shapes, such as a coin cell, cylindricalcell, or prismatic cell, for example.

The development of portable electronic devices and electrification oftransportation drive the need for high performance electrochemicalenergy storage. Small-scale (<100 Wh) to large-scale (>10 KWh) devicesprimarily use lithium-ion (Li-ion) batteries over other rechargeablebattery chemistries due to their high-performance.

The anode 101 and cathode 105, along with the current collectors 107Aand 107B, may comprise the electrodes, which may comprise plates orfilms within, or containing, an electrolyte material, where the platesmay provide a physical barrier for containing the electrolyte as well asa conductive contact to external structures. In other embodiments, theanode/cathode plates are immersed in electrolyte while an outer casingprovides electrolyte containment. The anode 101 and cathode areelectrically coupled to the current collectors 107A and 107B, whichcomprise metal or other conductive material for providing electricalcontact to the electrodes as well as physical support for the electrodecoating layer in forming electrodes.

The configuration shown in FIG. 1 illustrates the battery 100 indischarge mode, whereas in a charging configuration, the load 109 may bereplaced with a charger to reverse the process. In one class ofbatteries, the separator 103 is generally a film material, made of anelectrically insulating polymer, for example, that prevents electronsfrom flowing from anode 101 to cathode 105, or vice versa, while beingporous enough to allow ions to pass through the separator 103.Typically, the separator 103, cathode 105, and anode 101 materials areindividually formed into sheets, films, or electrode coating layercoated foils. Sheets of the cathode, separator and anode aresubsequently stacked or rolled with the separator 103 separating thecathode 105 and anode 101 to form the battery 100. In some embodiments,the separator 103 is a sheet and generally utilizes winding methods andstacking in its manufacture. In these methods, the anodes, cathodes, andcurrent collectors (e.g., electrodes) may comprise films.

In an example scenario, the battery 100 may comprise a solid, liquid, orgel electrolyte. The separator 103 preferably does not dissolve intypical battery electrolytes such as compositions that may comprise:Ethylene Carbonate (EC), Fluoroethylene Carbonate (FEC), PropyleneCarbonate (PC), Dimethyl Carbonate (DMC), Ethyl Methyl Carbonate (EMC),Diethyl Carbonate (DEC), etc. with dissolved LiBF4, LiAsF6, LiPF6, andLiClO4 etc. In an example scenario, the electrolyte may comprise Lithiumhexafluorophosphate (LiPF6) and lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI) that may be used together ina variety of electrolyte solvents. Lithium hexafluorophosphate (LiPF6)may be present at a concentration of about 0.1 to 4.0 molar (M) andlithium bis(trifluoromethanesulfonyl)imide (LiTFSI) may be present at aconcentration of about 0 to 4.0 molar (M). Solvents may comprise one ormore of ethylene carbonate (EC), fluoroethylene carbonate (FEC) and/orethyl methyl carbonate (EMC) in various percentages. In someembodiments, the electrolyte solvents may comprise one or more of ECfrom about 0-40%, FEC from about 2-40% and/or EMC from about 50-70% byweight.

The separator 103 may be wet or soaked with a liquid or gel electrolyte.In addition, in an example embodiment, the separator 103 does not meltbelow about 100 to 120° C., and exhibits sufficient mechanicalproperties for battery applications. A battery, in operation, canexperience expansion and contraction of the anode and/or the cathode. Inan example embodiment, the separator 103 can expand and contract by atleast about 5 to 10% without failing, and may also be flexible.

The separator 103 may be sufficiently porous so that ions can passthrough the separator once wet with, for example, a liquid or gelelectrolyte. Alternatively (or additionally), the separator may absorbthe electrolyte through a gelling or other process even withoutsignificant porosity. The porosity of the separator 103 is alsogenerally not too porous to allow the anode 101 and cathode 105 totransfer electrons through the separator 103.

The anode 101 and cathode 105 comprise electrodes for the battery 100,providing electrical connections to the device for transfer ofelectrical charge in charge and discharge states. The anode 101 maycomprise silicon, carbon, or combinations of these materials, forexample. Typical anode electrodes comprise a carbon material thatincludes a current collector such as a copper sheet. Carbon is oftenused because it has excellent electrochemical properties and is alsoelectrically conductive. Anode electrodes currently used in rechargeablelithium-ion cells typically have a specific capacity of approximately200 milliamp hours per gram. Graphite, the electrode coating layer usedin most lithium ion battery anodes, has a theoretical energy density of372 milliamp hours per gram (mAh/g). In comparison, silicon has a hightheoretical capacity of 4200 mAh/g. In order to increase volumetric andgravimetric energy density of lithium-ion batteries, silicon may be usedas the electrode coating layer for the cathode or anode. Silicon anodesmay be formed from silicon composites, with more than 50% silicon, forexample.

Si is one of the most promising anode materials for Li-ion batteries dueto its high specific gravimetric and volumetric capacity and lowlithiation potential (<0.4 V vs. Li/Li+). Upon lithiation, Si anodesdeliver high specific capacity (e.g. ca. 3572 mAh/g for Li15Si4), whichis particularly attractive for developing high capacity, high energydensity, and light weight Li ion batteries.

In an example scenario, the anode 101 and cathode 105 store the ion usedfor separation of charge, such as lithium. In this example, theelectrolyte carries positively charged lithium ions from the anode 101to the cathode 105 in discharge mode, as shown in FIG. 1 for example,and vice versa through the separator 105 in charge mode. The movement ofthe lithium ions creates free electrons in the anode 101 which creates acharge at the positive current collector 107B. The electrical currentthen flows from the current collector through the load 109 to thenegative current collector 107A. The separator 103 blocks the flow ofelectrons inside the battery 100, allows the flow of lithium ions, andprevents direct contact between the electrodes.

While the battery 100 is discharging and providing an electric current,the anode 101 releases lithium ions to the cathode 105 via the separator103, generating a flow of electrons from one side to the other via thecoupled load 109. When the battery is being charged, the oppositehappens where lithium ions are released by the cathode 105 and receivedby the anode 101.

The materials selected for the anode 101 and cathode 105 are importantfor the reliability and energy density possible for the battery 100. Theenergy, power, cost, and safety of current Li-ion batteries need to beimproved in order to, for example, compete with internal combustionengine (ICE) technology and allow for the widespread adoption ofelectric vehicles (EVs). High energy density, high power density, andimproved safety of lithium-ion batteries are achieved with thedevelopment of high-capacity and high-voltage cathodes, high-capacityanodes and functionally non-flammable electrolytes with high voltagestability and interfacial compatibility with electrodes. In addition,materials with low toxicity are beneficial as battery materials toreduce process cost and promote consumer safety.

The performance of electrochemical electrodes, while dependent on manyfactors, is largely dependent on the robustness of electrical contactbetween electrode particles, as well as between the current collectorand the electrode particles. The electrical conductivity of siliconanode electrodes may be manipulated by incorporating conductiveadditives with different morphological properties. Carbon black(SuperP), vapor grown carbon fibers (VGCF), and a mixture of the twohave previously been incorporated separately into the anode electroderesulting in improved performance of the anode. The synergisticinteractions between the two carbon materials may facilitate electricalcontact throughout the large volume changes of the silicon anode duringcharge and discharge.

State-of-the-art lithium-ion batteries typically employ agraphite-dominant anode as an intercalation material for lithium. Withdemand for lithium-ion battery performance improvements such as higherenergy density and fast-charging, silicon is being added as an electrodecoating layer or even completely replacing graphite as a dominant anodematerial. Most electrodes that are considered “silicon anodes” in theindustry are graphite anodes with silicon added in small quantities(typically <20%). These graphite-silicon mixture anodes must utilize thegraphite, which has a lower lithiation voltage compared to silicon; thesilicon has to be nearly fully lithiated in order to utilize thegraphite. Therefore, these electrodes do not have the advantage of asilicon or silicon composite anode where the voltage of the electrode issubstantially above 0V vs Li/Li+ and thus are less susceptible tolithium plating. Furthermore, these electrodes can have significantlyhigher excess capacity on the silicon versus the opposite electrode tofurther increase the robustness to high rates.

As discussed in the present disclosure, lithium-ion batteries withsilicon-dominant anodes show much higher rate performance compared tographite anodes, with ˜10C charge rates possible.

Silicon-based anodes have a lithiation/delithiation voltage plateau atabout 0.3-0.4V vs. Li/Li+, which allows it to maintain an open circuitpotential that avoids undesirable Li plating and dendrite formation.While silicon shows excellent electrochemical activity, achieving astable cycle life for silicon-based anodes is challenging due tosilicon's large volume changes during lithiation and delithiation.Silicon regions may lose electrical contact from the anode as largevolume changes coupled with its low electrical conductivity separate thesilicon from surrounding materials in the anode.

In addition, the large silicon volume changes exacerbate solidelectrolyte interphase (SEI) formation, which can further lead toelectrical isolation and, thus, capacity loss. Expansion and shrinkageof silicon particles upon charge-discharge cycling causes pulverizationof silicon particles, which increases their specific surface area. Asthe silicon surface area changes and increases during cycling, SEIrepeatedly breaks apart and reforms. The SEI thus continually builds uparound the pulverizing silicon regions during cycling into a thickelectronic and ionic insulating layer. This accumulating SEI increasesthe impedance of the electrode and reduces the electrode electrochemicalreactivity, which is detrimental to cycle life.

Although there has been a significant amount of effort to developsilicon anodes, the primary focus of developing these anodes is indealing with the following three key issues: 1) siliconnanoparticles—the majority of the silicon-based anodes that have highsilicon content use silicon nanoparticles to alleviate the large volumeexpansion. Nano-silicon is expensive and generally requires specialprocessing methods to prepare in large scale, which are not costeffective for large scale battery manufacturing; 2) carbonadditives—typical Si anode fabrication involves the use of carbonadditives and binders that required organic solvents. These solvents aretoxic and required solvent recovery systems to minimize the adverseeffect on the environment. Thus, compared with graphite anodes, whichuses water as the solvent, Si anode production is generally moreexpensive; and 3) non-conducting binder material—the final anodeformulation still contains non conducting polymeric binder that does notcontribute to the electrochemical performance. As a result of this “deadweight” of the binder, the improvement of gravimetric energy density ofthe resulting cells may be limited.

As discussed above, compared with graphite anodes, Si shows asignificant volume change during lithiation and de-lithiation, whichleads to pulverization of Si based anodes. Thus, having a mechanicallyrobust and electrochemically stable anode is desirable for improving theperformance of Si anodes. The high-capacity fade of Si based anodes isdirectly related to the large volumetric expansion of Si during thecharging and discharging (˜400%). As a result of pulverization, Si formselectrically isolated islands within the electrode. Continuous decreaseof the utilization of Si leads to rapid capacity decay over long termcycling. Additionally, the stress and strain developed in Lithiumsilicide (LixSi) disrupts the SEI layer on Si particles resultingcontinuous formation of new SEI layer. To meet the high energy demand ofEV (Electric Vehicle) industry for lighter batteries with longer drivingrange and cycling life, focus has been on improving performance of Sianodes.

Among the recent advancements in silicon-based anode development, one isthe direct coated anode using organic solvent-based binders followed byheat treatment to convert the binder into a carbon matrix. However, useof the organic solvents is problematic, as discussed above. In thepresent disclosure a direct coated anode using aqueous-based bindersfollowed by heat treatment to convert the binder to carbon matrix isdisclosed. The present disclosure addresses the following keyadvancements: 1) use of environmentally friendly solvent (water) toallow safer, cheaper and faster processing and scalability, specificallyanode roll-to-roll fabrication; 2) Si dominant anodes with high Sicontent (>70 wt. %) for high capacity; and 3) the development of Sidominant anodes free of non-conducting binders capable of fast charging(>2C), i.e. anodes that contain only carbon and silicon. Althoughsolvent-based anodes have had some effectiveness in improving cycleperformance, these anodes may have weak adhesion to the currentcollector and contain non-continued carbon media that leads tounacceptable performance. Also, although the introduction of carbonadditives can somewhat improve the conductivity of the anode, theexistence of carbon additives may weaken the adhesion of anode materialsto the current collector. Thus, the binder plays an important role inimproving the performance of silicon anodes.

Currently, polymeric binders may be used in anode technologies tomaintain the integrity of the anode during excessive volume changesduring lithiation. For example, polyvinylidene difluoride (PVDF) iscommonly used as a binder in graphite cells, but it is not capable ofhandling the excessive volume changes of silicon. Additionally, PVDF issoluble only in toxic organic solvents such as NMP, which requiresolvent recovery systems to recycle the solvent. Binders such ascellulose may also be used in conventional electrodes. However, thesebinders have not been successfully used in Si dominant anodes since thepolymer interconnection between Si and carbon additives are not strongenough for excessive volume changes of Si. Additionally, most of thepolymeric binders are soluble only in toxic organic solvents (e.g.,NMP).

Some water-based polymers such as carboxymethyl cellulose (CMC),sucrose, poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), starch,chitosan, lignin, and gums (e.g., xanthan gum) have been used as bindersfor preparing Si anodes. However, these polymers have not created asuccessful binder system that shows superior electrochemical performanceand is capable of large-scale production.

In the present disclosure, water-soluble (aqueous-based) PAA-basedpolymeric binders that are capable of mitigating the capacity fade of Sianodes occurring at a high rate and long-term cycling are disclosed. ThePAA-based polymers may be polymer blends that include PAA as the mainpolymeric matrix while introducing aqueous based polymers as a secondarycomponent. In some embodiments, the PAA may be combined with phenolicresin (PAA-phenolic or PAA-phenolic resin, for short). The processesinvolve include, but are not limited to, the steps of synthesizingpolymers and optimization of water solubility; creating aqueous basedsolutions for electrode preparation; carbonization of the water-solublebinder incorporated in Si dominant anode; preparing polymer blends withadditional polymer components such as phenolic resin (e.g., creatingPAA-phenolic) using water as the solvent and the preparation of slurrieswith Si; using such slurries for coating of Si dominant anode;electrochemical studies of PAA-phenolic binders with Si dominant anode.The polymer blend binders (such as phenolic-PAA binders) may be used forall different types of Si or SiOx anodes with or without a conductive(e.g. graphite) additive.

In one embodiment, a battery electrode is disclosed where the electrodecomprises an electrode coating layer on a current collector, theelectrode coating layer formed from silicon and a water solublePAA-based polymer blend, wherein the water soluble PAA-based polymerblend comprises PAA and one or more additional water-soluble polymercomponents. In a further embodiment, the one or more additionalwater-soluble polymer components may be phenolic resin, and theconcentration of the phenolic resin in the water soluble PAA-basedpolymer blend may be <30 wt. %. In further embodiments, the one or moreadditional water-soluble polymer components comprises a polymercontaining one or more functional groups selected from the groupconsisting of —OH, NH—, NH₂, and —COOH. In another embodiment, anelectrode is disclosed where the electrode comprises an electrodecoating layer on a current collector, the electrode coating layer formedfrom silicon and a water soluble PAA-based polymer blend, wherein thewater soluble PAA-based polymer blend is a tertiary system comprisingPAA and two additional water-soluble polymer components. IN a furtherembodiment, the tertiary system may comprise PAA, phenolic resin and athird water-soluble polymer component.

Water-based anode fabrication is of interest for large scalemanufacturing of anodes to reduce the cost and eliminate the use oftoxic solvents. Objectives of a water-based anode polymer include: 1)ease of processing-the resin being highly soluble in water allowing forease of adjusting viscosity during coating; 2) high carbon yield andfilm-forming properties upon pyrolysis to create a conductive matrixaround and between silicon particles; 3) a homogeneous distribution ofpolymeric components in water and the slurry without phase separationduring the slurry formulation or coating; and 4) possessing a relativelylow pyrolysis temperature that is compatible with the thermal behaviorof the associated current collector. Carbonization or pyrolyzationtemperature may be temperatures 200-1084° C. (melting point of copper).In some embodiments, the pyrolyzation temperature may be temperatures400-1000° C. In other embodiments, the pyrolyzation temperature may betemperatures 400-800° C. The atmosphere for pyrolysis may be a singlegas or mixture of inert or reactive gas or gases.

Some commercially available water-soluble polymers have significantlylow carbon yield (<10 wt. %) and develop microcracks during pyrolysis.As a result, those water-soluble polymers exhibit poor mechanicalproperties in the anode after pyrolysis. Therefore, these polymers arenot suitable for achieving mechanically stable Si dominant anodes aftercarbonization. Polymer resins and their derivatives with high carbonyield upon pyrolysis are desired to yield a continuous carbon mediumwhile keeping the robustness of the anode. Although available polymersand their blends may be capable of achieving a high char yield, most ofthese polymers are insoluble in water. PAA itself has a very low charyield, i.e. pyrolytic carbon yield is ˜<5-15% upon pyrolysis. Thus thesignificant loss of the material upon pyrolysis is a challenge whenusing it as a precursor to generate a pyrolyzed carbon binder.

Carbon media presence in the anode matrix plays a crucial role inphysical and electrochemical stability of the Si dominant anodes. In thepresent disclosure, a commercially viable Si dominant anode thatcontains a carbon matrix that acts as both the binder and the conductingagent is disclosed (this is sometimes referred to as a “binder-free”anode as there is no separate binder). Elimination of non-conductingbinder significantly improves the cycling performance and high-ratecapabilities while keeping the mechanical integrity of the anode. Makinganodes using aqueous-based polymers and subsequent conversion of thepolymer to carbon source can reduce the cost and improve the Si anodeperformance.

In the present disclosure, water-soluble polymeric binder materials aredescribed. These water-soluble polymeric binders allow for preparationof “binder-free” anodes and have the following advantages:

-   -   1) Easy to process: The polymer/polymeric blend may be highly        soluble in water allowing for ease of optimizing rheological        properties of the slurry.    -   2) High carbon yield and retaining electrode structure upon        pyrolysis: The carbon matrix may provide conductive pathways        around and between Si particles.    -   3) Fully miscible: The nature of the miscibility of the        polymeric components in water allows for creation of the slurry        without phase separation during the slurry preparation, coating        and drying.    -   4) Favorable pyrolyzation temperature: Possess a relatively low        pyrolyzation temperature to avoid thermal decomposition/the loss        of mechanical properties of the current collector.

Polymers are created from monomers and the molecular weight (MW) of apolymer is based on the identity of the monomer and the number ofmonomers present in the polymer molecule. Polymer molecular weights areusually given as averages and may fall in a distribution. The MWdistribution determines the properties of the polymer. In themeasurement of the average MW, the two most common ways to measure areMn, number averaged MW, and Mw, weight averaged MW (midpoint of thedistribution in terms of the number of molecules). Polydispersity of apolymer (Mw:Mn ratio) describes the distribution width. Other ways tocalculate MW include viscosity average molecular weight (Mv), and higheraverage molecular weight (Mz, Mz+1). The choice of method for polymermolecular weight determination depends on factors such as cost,experimental conditions and requirements. Degree of polymerization isalso often used in discussing polymers; this is the average number ofmonomeric units per molecule.

In this disclosure, a PAA-based polymer binder is described that has thefollowing features:

-   -   1) Blend of two or more polymer compounds.    -   2) Fully water soluble (aqueous-based) and does not separate        after introduction of Si and water.    -   3) Has high char yield after carbonization.    -   4) Able to form a stable, Si dominant anode after carbonizing        binder and Si mixture.

In the present disclosure, water soluble PAA-based binders are describedthat are made by starting with the primary component of poly(acrylicacid) (PAA) as shown below:

The presently disclosed PAA-based polymer binders are a blend thatcontains one or more additional water-soluble polymer components inaddition to the PAA. In some embodiments, a resin is utilized as thesecondary component in the blend; this component may contain phenolictype resins such as resol (other inorganic materials such as salts mayalso be present) to improve the water solubility and water tolerance(the highest amount of water that can be introduced before phaseseparation). These phenolic type resins are capable of crosslinking withwater-soluble polymer derivatives containing hydrophilic functionalgroups such as PAA. The use of secondary or tertiary water-solublepolymeric components can significantly improve the stability of thePAA-based polymer blend compared to unmodified resins. PAA alone(without a secondary or tertiary polymer added) has low carbon yield andshows significant loss of the weight of PAA at high temperatures (>200°C.). Therefore, introducing a high char yield polymer, such as aphenolic resin (>50% or >60% or >70%) to the PAA solution results in apolymer blend (PAA-phenolic) that has a much higher char yield (amountof pyrolytic carbon) compared to neat PAA polymer.

As discussed above, neat PAA polymer primarily undergoes thermaldecomposition reactions (releasing H₂O and gaseous products) at hightemperature (pyrolysis). However, the creation of a polymer blend byutilizing PAA plus additional polymers including, but not limited to,phenolic resins, may bypass the direct decomposition of PAA and initiatepolycondensation reactions between the phenolic resin and PAA beforepyrolysis. This reaction may be important to form a new covalentlybonded polymer (formed from the reaction between the PAA and thephenolic resin) that can generate higher char-yield and a more stablecarbon matrix upon pyrolysis. This new polymer may also combine, mix, orfurther react with any excess PAA through a further polycondensationreaction.

One such polymer blend of water soluble PAA and phenolic resin may yielda pyrolytic carbon >20 wt. % (See FIG. 7 ). When controlling the ratioof PAA:phenolic resin, the pyrolytic carbon yield may vary between 20-50wt. % or >50 wt. %. This combination of PAA and phenolic resin resultsin higher char-yield than that of neat PAA upon pyrolysis, which in turnmay be more cost-effective. Also, the PAA and phenolic resin blend maygenerate a more mechanically stable carbon matrix upon pyrolysis thatcan hold active materials together during electrochemical cycling. Thismay provide better mechanical strength due to increased stability of thematrix.

In one embodiment, a binder-free Si dominant (>70 wt. %, >50 wt. %)electrode is fabricated using a slurry of a water-soluble polymer blendincluding PAA as the main component plus a secondary polymer componentof phenolic/resol polymer resin. The polymer blend serves as both thebinder and carbon matrix. These water-based anode slurries may possesshigh viscosity and can be further optimized. The resulting Si anodesretain their stable electrode structure upon heattreatment/pyrolyzation/carbonization. The amount of phenolic content canbe <50 wt. %, <40 wt. %, <30 wt. %, <2 wt. % or <10 wt. % w.r.t thetotal weight of the polymer blend.

Among other polymer derivatives that may be used as a secondary ortertiary component in a water soluble PAA-based binders, phenolic resinsare particularly attractive since they have high molecular weight andhigh char yield, which are ideal properties for adoption as binders forsilicon anodes. Phenolic resins (or phenol formaldehyde resins (PF))include synthetic resins such as those obtained by the reaction ofphenols with formaldehyde. Phenolic resins are divided into two maintypes, novolacs and resols. Novolacs are phenol-formaldehyde resins madewhen the molar ratio of formaldehyde to phenol is around one or lessthan one. Resols are phenol-formaldehyde resins are made with aformaldehyde to phenol ratio of greater than one (usually between about1.2-2, in some embodiments, around 1.2-1.7). Ortho, meta and paralinkages are contemplated, as well as linear and branched structures.Phenolic resins can have different molecular weights and degrees ofpolymerization depending on the reaction condition.

Novolac phenolic resins (may also be referred to as a phenolic/novolactype polymer) have phenolic units mainly linked by methylene groups.Water soluble novolac resins with different molecular weights may beused as a secondary polymer in the water soluble PAA-based binders. Anexample structure of a novolac phenolic resin is shown below (I):

In some embodiments, n may be >5; in other embodiments, n maybe >10, >50, >100, >500 or >1,000. Branched novolac types such asphenol-crotonaldehyde-resorcinol resins are also contemplated.

Resol phenolic resins (may also be referred to as a phenolic/resol typepolymer) may have methylene and/or ether bridges and have unreactedhydroxymethyl (—CH₂OH) groups. In some embodiments, the number of unitsin the resin may be >5; in other embodiments, the number of units maybe >10, >50, >100, >500 or >1,000. An example structure of a resolphenolic resin is shown below (II):

However, most phenolic resins typically do not readily dissolve in waterbut are soluble in alcohol and ketones. Some resol resins may beslightly soluble, but the solubility is generally low. Somewater-soluble phenols have very low water tolerance that leads to theformation of a separated polymer phase with the addition of water and/orprecipitation of the polymer after exceeding the phenolic:water weightratio. This may be an obstacle to water-based processing. Furtherreaction (e.g. derivatization) of the polymer backbone may alleviatethese problems.

As discussed above, the presently disclosed PAA-based polymer bindersare a blend that contains one or more additional water-soluble polymercomponents in addition to the PAA. This combination improves theproperties of the binder, including improving the miscibility of theadditional polymer components within the PAA polymer matrix andoptimizing the viscosity of the resulting slurry. The PAA-based polymerbinder may undergo two or more different stages of chemical changesbetween the components, such as (1) Van Der Waals type interaction(hydrogen bonding); and (2) thermal curing, where polycondensationreactions take place.

In one embodiment, PAA-based polymer binders may be a blend of PAA andphenolic resin. During initial mixing, the phenolic resin (polymer) andPAA form a miscible polymer blend. The phenolic polymer and PAA bothform hydrogen bonds (H-bonds) resulting in a stable polymeric blend.Then the as-prepared polymeric blend may be used as a binder forpreparing an electrode slurry with Si. These strong Van der Waals forcesfacilitates the formation of mechanically robust green anodes that canbe processable in both roll-to-roll and punched forms.

Further reaction of the blend may form covalent bonds. In one example,the PAA-phenolic resin blend described above may undergo apolycondensation reaction upon slow rate heat treatment, which thePAA-phenolic resin blend is converted to a co-polymeric form that haschemical bonds between the PAA and the phenolic resin polymer components(nominally forming a co-polymer). At elevated temperatures thermaldecomposition of the co-polymeric form leads to formation of partiallyreduced pyrolytic carbon. See FIG. 2 .

Further, in the presence of Si, in addition to polycondensationreactions, phenolic-PAA polymer blends may chemically interact with Si—Oon the surface of Si particles. The nature of strong chemical bonds thatare formed between the polymer components and the Si-polymer iscontrolled by the thermal curing (heating rate) stage.

FIG. 3A is a flow diagram of a direct coating process for fabricating acell with a silicon-dominant electrode, in accordance with an exampleembodiment of the disclosure. This process comprises physically mixingthe electrode coating layer and conductive additive together, andcoating it directly on a current collector as opposed to forming theelectrode coating layer on a substrate and then laminating it on acurrent collector. This strategy may also be adopted by otheranode-based cells, such as graphite, conversion type anodes, such astransition metal oxides, transition metal phosphides, and other alloytype anodes, such as Sn, Sb, Al, P, etc.

In step 301, the raw electrode coating layer may be mixed in a slurrycomprising, e.g. a PAA-phenolic resin blend polymeric binder. In themixing process, the active material may first be mixed, e.g., thebinder, a solvent, and conductive additives, if any. Then, siliconpowder with a 1-30 or 5-30 μm particle size may then be dispersed ate.g., 1000 rpm for, e.g., 10 minutes, and then the slurry may be addedand dispersed at, e.g., 2000 rpm for, e.g., 10 minutes to achieve aslurry viscosity within 1500-4000 cP and a total solid content of about30-40 wt. %.

The particle size (nano to micro) and mixing times may be varied toconfigure the electrode coating layer density and/or roughness.Furthermore, cathode electrode coating layers may be mixed in step 301,where the electrode coating layer may comprise lithium cobalt oxide(LCO), lithium iron phosphate, lithium nickel cobalt manganese oxide(NMC), Ni-rich lithium nickel cobalt aluminum oxide (NCA), lithiummanganese oxide (LMO), lithium nickel manganese spinel, LFP, Li-richlayer cathodes, LNMO or similar materials or combinations thereof, mixedwith carbon precursor and additive as described above for the anodeelectrode coating layer.

In step 303, the as-prepared slurry may be coated on a copper foil, 20μm thick in this example, and in step 305 may be dried at 130° C. in aconvection oven to dry the coating and form the green anode. Similarly,cathode electrode coating layers may be coated on a foil material, suchas aluminum, for example.

An optional calendering process may be utilized in step 307 where aseries of hard pressure rollers may be used to finish the film/substrateinto a smoother and denser sheet of material.

In step 309, the electrode coating layer may be pyrolyzed by heating to500-800° C., 650° C. in this example, in an inert atmosphere such thatcarbon precursors are partially or completely converted into conductivecarbon. The pyrolysis step may result in an anode electrode coatinglayer having silicon content greater than or equal to 50% by weight,where the anode has been subjected to heating at or above 400 degreesCelsius. In some embodiments, lower temperatures may be used.

Pyrolysis can be done either in roll form or after punching in step 311.If done in roll form, the punching is done after the pyrolysis process.In instances where the current collector foil is notpre-punched/pre-perforated, the formed electrode may be perforated witha punching roller, for example. The punched electrodes may then besandwiched with a separator and electrolyte to form a cell. In step 313,the cell may be subjected to a formation process, comprising initialcharge and discharge steps to lithiate the anode, with some residuallithium remaining, and the cell capacity may be assessed. The fabricatedanode shows superior adhesion to copper, a remarkable cohesion, andexceptional flexibility. This anode is shown to be capable of fastcharging and performs similar or better than current anodes.

FIG. 3B is a flow diagram of an alternative process for lamination ofelectrodes, in accordance with an example embodiment of the disclosure.While the previous process to fabricate composite anodes employs adirect coating process, this process physically mixes the activematerial, conductive additive if desired, and binder together coupledwith peeling and lamination processes.

This process is shown in the flow diagram of FIG. 3B, starting with step321 where the raw electrode coating layer may be mixed in a slurrycomprising phenolic-PAA polymeric binders. For example, PAA formspolymer blends readily with phenolic resins in DI water withoutgelling/phase separation and creates a viscous aqueous solution that canbe directly used for preparing the anode slurry.

The particle size and mixing times may be varied to configure theelectrode coating layer density and/or roughness. Furthermore, cathodeelectrode coating layers may be mixed in step 321, where the electrodecoating layer may comprise lithium cobalt oxide (LCO), lithium ironphosphate, lithium nickel cobalt manganese oxide (NMC), Ni-rich lithiumnickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO),lithium nickel manganese spinel, LFP, Li-rich layer cathodes, LNMO orsimilar materials or combinations thereof, mixed with carbon precursorand additive as described above for the anode electrode coating layer.

In step 323, the slurry may be coated on a polymer substrate, such aspolyethylene terephthalate (PET), polypropylene (PP), or Mylar. Theslurry may be coated on the PET/PP/Mylar film at a loading of 3-6 mg/cm2for the anode and 15-35 mg/cm2 for the cathode, and then dried in step325. An optional calendering process may be utilized where a series ofhard pressure rollers may be used to finish the film/substrate into asmoothed and denser sheet of material.

In step 327, the green film may then be removed from the PET, where theactive material may be peeled off the polymer substrate, the peelingprocess being optional for a polypropylene (PP) substrate, since PP canleave ˜2% char residue upon pyrolysis. The peeling may be followed by acure and pyrolysis step 329 where the film may be cut into sheets, andvacuum dried using a two-stage process (100-140° C. for 14-16 hours,200-240° C. for 4-6 hours). The dry film may be thermally treated at1000-1300° C. to convert the polymer matrix into carbon.

In step 331, the pyrolyzed material may be flat press or roll presslaminated on the current collector, where for aluminum foil for thecathode and copper foil for the anode may be pre-coated withpolyamide-imide with a nominal loading of 0.35-0.75 mg/cm² (applied as a5-7 wt % varnish in NMP, dried 10-20 hour at 100-140° C. under vacuum).In flat press lamination, the active material composite film may belaminated to the coated aluminum or copper using a heated hydraulicpress (30-70 seconds, 250-350° C., and 3000-5000 psi), thereby formingthe finished composite electrode. In another embodiment, the pyrolyzedmaterial may be roll-press laminated to the current collector.

In step 333, the electrodes may then be sandwiched with a separator andelectrolyte to form a cell. The cell may be subjected to a formationprocess, comprising initial charge and discharge steps to lithiate theanode, with some residual lithium remaining, and testing to assess cellperformance.

In accordance with the disclosure, PAA may be reacted with phenolicresins such as (I) or (II) above, which significantly increases theirsolubility in water. The reaction creates a phenolic-PAA polymericblend, which can be used in fabricating an electrode, for example, bythe procedures above.

Anodes fabricated using these binders are capable of fast charging andmay show improved cycling performance compared to the currenttechnologies, which use binders that are only soluble in organicsolvents.

Poly(acrylic acid) (PAA) may be reacted with phenolic resin typepolymers in ratios where the ratio of phenolic:PAA may be from about 1:1to about 1:10. In some embodiments, the ratio of phenolic:PAA may befrom about 1:1 to about 1:5; in other embodiments, the ratio ofphenolic:PAA may be from about 1:1 to about 1:3. In one embodiment, thephenolic:PAA ratio may be about 1:2.45 (e.g. Table 1) and in anotherembodiment, the phenolic:PAA ratio may be about 1:3.67 (e.g. Table 2).

Solutions of PAA in water are used for the reaction and theconcentration may be from about 2 wt % to about 20 wt %. In someembodiments, the wt % of the PAA in water is from about 5 wt % to about15 wt %; in other embodiments, the wt % of the PAA in water is fromabout 10 wt % to about 15 wt %.

In a preferred embodiment, the solid content of the starting phenolicresin in H₂O (as received) may be >50 wt. % and the PAA solution may be<50 wt. % to avoid the phase separation between the phenolic resin andthe PAA. In a further preferred embodiment, the composition of thephenolic resin may be <30 wt. % of the total phenolic-PAA polymer blend,to achieve a slurry viscosity 1500-2000 cps. Further, when making theelectrode slurry, mixing of high solid content phenolic resin solutions(in water) into low solid content PAA solutions (in water) prior toadding Si may be preferred as this facilitates the formation of amiscible phenolic-PAA resin blend.

In one embodiment, a phenolic (resol) resin type polymer (Plenco 15637aqueous resol resin liquid) may be reacted with poly(acrylic acid) (PAA)in the ratio phenolic:PAA of 1:2.45. The starting wt % of the PAA can be10%, 20%, or <50% (with respect to the total weight of the final resincomposite) in deionized (DI) water. Other water based crosslinked orun-crosslinked phenolic resins may also be used.

An exemplary binder formula for a phenolic resin-PAA polymeric blend isshown in Table 1, below. In this embodiment, 12 wt. % PAA in DI waterwas used to prepare the polymer blend solution.

TABLE 1 Phenolic-PAA resin composition used as the binder to prepareaqueous based anodes Phenolic/Resol PAA 1 2.450 Phenolic resin (g) 10.2PAA (g) 166

Mixing of PAA with phenolic resin forms polymer blends readily withdeionized (DI) water without gelling/phase separation and forms aviscous solution of the polymer binder that can be directly used toprepare the anode slurry. A prepared anode slurry may be used as acoating on Si dominant anodes. In this embodiment (formulation of Table1), the slurry may be formulated to obtain the final anode compositionof Si:Carbon (90:10 W/W) after pyrolysis/carbonization. Roll-to-rollcoating of Si dominant anodes can be performed using aqueous basedphenolic-PAA polymer blend and water (as the solvent). Green Si anodesmay be pyrolyzed at 650° C. for 3 hours under Argon atmosphere. See FIG.4 .

Coated Si anodes show densely packed Si particles that are embedded inthe phenolic-PAA polymer blend. SEM images show polymer blend isuniformly distributed among Si particles (FIG. 3 ). Upon pyrolyzation,the Si anode may become porous and the polymer blend may convert to acarbon matrix, which provides conductive pathways between Si particlesand the current collector. See FIG. 5 . The as-coated Si anode isdenoted as “green anode”.

FIG. 6 is a plot showing a comparison of the capacity retention of astandard anode (dotted line) versus an anode prepared using thephenolic-PAA polymer blend (solid line) from Table 1. Cellconfiguration: Si anode//NCM811 cathode full cells. The plot containsdata from 3 cells per group. The onset image shows a digital photographof the final pyrolyzed Si anodes prepared using the aqueous basedphenolic-PAA binder and water (solvent). The anode using thephenolic-PAA binder exhibits higher initial capacity than that of thestandard anode. The phenolic:PAA ratio of the binder used to preparethese anodes is 1:2.45 (wt/wt).

TGA data illustrates that the char yield of the phenol-PAA polymer blendfrom Table 1 at 650° C. is ˜22 wt. %. See FIG. 7 . As discussed above,this demonstrates the aqueous based phenolic-PAA binder having a muchhigher char-yield than that of PAA alone.

FIG. 8 is a plot showing a comparison of as prepared Si anodes (Table 1)using aqueous based phenolic-PAA binders compared with a standard Sianode prepared using NMP as the solvent (FIG. 5 ). The Si anodesprepared using the aqueous based phenolic-PAA binder showed highercoulombic efficiency. Without being bound to the theory or mode ofoperation, it is believed that this is mainly due to the graphiticnature of the pyrolytic carbon obtained with the phenolic-PAA binder.The plot contains data from 3 cells per group.

In another embodiment, the phenolic:PAA ratio may be increased (morePAA). An exemplary binder formula for a phenolic resin-PAA polymericblend with an increased ratio is shown in Table 2, below. In thisembodiment, 12 wt. % PAA in DI water may be used to prepare the polymerblend solution. In this example, the PAA content of the polymer resinwas increased compared to the Example shown in FIG. 6 (and Table 1).

TABLE 2 Phenolic-PAA resin composition used as the binder to prepareaqueous based anodes Phenolic/Resol PAA 1 3.670 Phenolic resin (g) 10.2PAA (g) 249

In FIG. 9 and FIG. 10 , cycling data for aqueous based anodes preparedusing phenolic-PAA resin compositions from both Table 1 (1:2.45 wt/wt)and Table 2 (1:3.67 wt/wt) as the binder in Si anode is shown. FIG. 9shows the normalized capacity retention and FIG. 10 shows the internalresistance for 60 s pulses during charge for aqueous based anodesprepared using phenolic-PAA with a 1:3.67 wt/wt ratio as the binder inSi anode as compared to anodes prepared using phenolic-PAA with a 1:2.45wt/wt ratio. This data illustrates that increasing the PAA content inphenolic-PAA resin did not adversely affect the anode throughresistance. The anodes prepared using higher PAA content in the resinhave a slight improvement in the cycle life compared to the anodesprepared using lower PAA content.

The incorporation of more PAA does not adversely affect the cellcharacteristics. FIG. 10 shows a similar increase in cycling resistancefor both versions of resin with phenolic-PAA.

Table 3 compares through resistance values of the Si anodes (afterpyrolysis) prepared using two different phenolic-PAA resins having thedifferent phenolic:PAA ratios shown in Tables 1 and 2.

TABLE 3 Resistance values for phenolic-PAA resin based anodes afterpyrolysis Resistance of the Resin Examples anodes (Ohm) Phenolic:PAA0.44 (1:2.45) Phenolic:PAA 0.42 (1:3.67)

In some embodiments, 28.9 wt. % and 21.4 wt. % of phenolic resin wasintroduced to a PAA solution (12 wt. % in H₂O), to create the blends inwhich the phenolic:PAA resin is 1:2.45 wt/wt and 1:3.67 wt/wt of thetotal amount of polymer respectively. The presence of PAA helps to forma uniform slurry without phase separation as well as improving thecycling performance.

Other polymers that may be included in the polymer blends (with the PAA)include, but are not limited to, one or more of polyvinyl alcohol (PVA),polyvinylpyrrolidone (PVP), poly aminoacids, polyglycolides (PG),polyethylene glycol (PEG), and co-polymers such asPoly(ethylene-co-acrylic acid). Additionally, PAA may be further reactedand/or a third component may be utilized. In one embodiment, other waterbased crosslinked or un-crosslinked phenolic resins are used inconjunction with PAA to create water soluble polymer blends for use asbinders.

In some embodiments, the polymer blend comprises one, two or morepolymeric components, which can be designated as binary, tertiary, ormore. In one embodiment, the binder includes PAA, phenolic resin and athird component, creating a tertiary system.

An example of a tertiary system may be made as follows: PAA and phenolicresin (phenolic-PAA) may be combined with aqueous based PAI as atertiary polymeric component. The PAI component may be Al-30 polymer(Torlon® Al-30 which is a wet polymer granule developed for theperformance coating industry comprised mainly of polyamide-imide as thesolid), added as ˜5 wt. % in the slurry formulation and 1 wt. % w.r.tfinal anode loading after pyrolyzation. Aqueous based anodes containingAl-30 have shown improved mechanical properties, thus providing improvedadhesion and cohesion of the anodes without adversely affecting thecycle life. Fast charging cycling (@ 2C) of anodes made from thetertiary polymeric system phenolic-PAA+Al30 showed improved cyclingperformance compared with NMP based anodes. See FIG. 11 whichillustrates the 2C cycling data for aqueous based anodes prepared usingphenolic-PAA+Al30 vs. NMP based anode.

Other polymers used in the blends may comprise reactive functionalgroups such as —OH, NH—, NH₂, —COOH which may be decomposed at arelatively low temperature (below decomposition temperature of phenols).

Decomposable functional groups may generate gaseous byproducts, whichmay leave additional pore structures within the anode. In someembodiments, the presence of these pores may provide void space requiredfor rapid volume changes of Si during lithiation and de-lithiation.Additionally, these pores may improve electrolyte wettability and ionicconductivity of the anodes.

In additional embodiments, the polymers in the polymer blend (e.g. PAAor other components) may be reacted with further polymer componentscontaining carboxylic acid, alcohol or amine functional groups, whichmay further improve the adhesion of the anode material to the currentcollector. Functional groups such as —COOH and —NH₂ in combination withphenolic-PAA polymer blend, can promote crosslinking in the polymerblend (by reaction of the functional groups). Crosslinking reactions maybe initiated in the presence of an inorganic salt, catalyst or highenergy radiation.

The presence of carboxylic acid groups in the binder may participate insurface treatment/roughening of the Cu current collector. Additionally,these functional groups may further improve particle-to-particleinteractions which are necessary to retain the electrode structureduring pyrolysis and during cycling.

Some polymer components containing acidic functional groups that may bereacted include but are not limited to maleic acid (or maleic acidderivatives) or anhydrides such as maleic anhydride (e.g. Succinicanhydride, Hexanoic anhydride, Propionic anhydride, Myristic anhydride,Acrylic anhydride, (2-Dodecen-1-yl)succinic anhydride,2,3-Dimethylmaleic anhydride) as illustrated by the structures below:

Anhydrides rapidly create an acidic group in the presence of water.These organic acids can be added to the slurry as an additive to improvethe rheological properties of the slurry and final anode.

Other polymer components that may be used to react include but are notlimited to compounds containing amine functional groups (e.g. Chitosan,Poly(allylamine), Polyethylenimine (PEI), JEFFAMINE, Zytel, Selar PA)containing amine functional groups such as NH₂ groups as illustrated bythe structure below:

Other functional aliphatic and aromatic amine compounds of differentmolecular weights are contemplated.

The other components may react with polymer blend components to make aderivative. In some embodiments, derivatives may be made using groupssuch as —COOH, and/or —CO—NH₂ groups, etc. In some embodiments, theexisting polymer backbone(s) may be used for further reactions to makevarious binder structures. Depending on the specific derivatizationand/or blends that are created, water solubility (water tolerability)can be tailored to achieve desired binder properties required for Sianodes. In some embodiments, a phenolic/resol type polymer is used asthe starting material.

Polymer blend components such as phenolic resins can be derivatized byreacting, and/or can be included in a polymer blend by addition ofpolymer additives. The phenolic resin derivatives have increased watersolubility. One reaction used to derivatize the phenolic resins iscrosslinking. Crosslinking is the process of forming chemical bonds tojoin (or bridge) two or more polymer chains. Crosslinking can occur whenpolymers are reacted, either internally, or with other compounds thathave functional groups (crosslinking group). Crosslinking can occur bybridging with methyl, ethyl, ether, carboxylate, ester, amide, or anyother functional groups that can contribute to form a polymeric network.

In one embodiment of this disclosure, a binder-free Si dominant (>70 wt.%, >50 wt. %) electrode is fabricated using water-soluble derivatives orblends of phenolic polymer resins with PAA. The water solublederivatives or blends of phenolic polymer resins are created fromdifferent water-soluble polymer crosslinkers or additives. Thesewater-based slurries may possess high viscosity and result in highcarbon yield upon heat treatment/pyrolysis while retaining the electrodestructure.

As discussed above, formaldehyde may be present in a phenolic resin usedin a polymer blend for an anode active material slurry, where the degreeof the presence of formaldehyde in the phenolic resin may range from1:0.5 to 1:2 (phenol to formaldehyde) during synthesis. The synthesis ofphenolic binders may be tailored to optimize the water tolerance(solubility/dispersibility), solid content, and viscosity of thephenolic resin. The water tolerance of phenolic resin can be 10-80%w.r.t. phenolic resin content before a phase separation in water occurs.Phenolic resin may contain 1-10 wt %, 10-25 wt %, or 25-90 wt %. Theamount of binder resin required to achieve the desired carbon wt % afterpyrolysis is significantly lowered as the initial solid content and charyield of the phenolic resin-polymer conjugated resin is higher than thecommon water soluble polymer binders. The water solubility and viscosityof the phenolic resin may be configured to achieve desired slurryviscosity via crosslinking with one or more water soluble polymers. Inone embodiment, the water tolerance of a phenolic/resol type polymer canbe optimized during synthesis of the polymer, as described above.

In another example scenario, unmodified phenolic resins may be utilizedwithout the aforementioned crosslinking polymers, their derivatives, andtheir combinations for all different types of Si or SiO_(x) anodes.Furthermore, the crosslinked polymers, their derivatives, and theircombinations may be used without pyrolysis for electrode preparation.The above phenolic resins also can be expanded to use with coated typeSi/SiO_(x). Coating materials can be raging from conductive carbon toceramic coating. The final slurry prepared using the above may containsecondary electroactive/inactive components that may support theperformance of the anode.

Conductive additives which may minimize the isolation of Si particles,such as Super P, carbon black, graphite, graphene, carbon nano/microfibers, carbon nanotubes, porous (meso/macro) carbons and other types ofone-, two-, three-dimensional carbon materials can be introduced intoall of the aforementioned binders. Similarly, metallic nano/microparticle, fibers, wires and other types of one-, two-, three-dimensionalstructures may be introduced into all different aforementionedcrosslinked polymers, their derivatives, and their combinations.

Water based crosslinked phenolic resins with high char yield uponpyrolysis at temperatures >200° C. may be utilized with the PAA tocreate a polymer blend for an electrode binder. These polymer blends canundergo curing before pyrolysis to form a re-arranged polymeric network.The preparation of polymers may comprise many decomposable functionalgroups such as —OH, NH—, NH₂, —COOH at a relatively low temperature,below the decomposition temperature of phenols. These groups cangenerate gaseous byproducts that can create nano to micro pores withinthe anode/carbon media. The presence of these pores may facilitate therapid volume changes of silicon microparticles during cycling as well aselectrolyte soaking to improve ionic conductivity of the anodes.

The presence of functional groups such as —COOH and —NH₂ may promote thecrosslinking with the functional groups in the polymer blends (various—OH and —O—). In addition, in-situ crosslinking via thermal and/orphotochemical crosslinking of phenol or phenolic type polymer resins inthe presence of a second water-soluble polymer may occur with thesematerials. The crosslinking reaction may be initiated in the presence ofan inorganic salt or catalyst or photochemically.

Strong hydrogen bonds associated with —COOH groups may improve theparticle-particle affinity. The existence of strong chemical bonds inthe slurry form is utilized to create a carbon matrix that stronglyadheres to the particles. New bonds may be formed between particles andthe copper surface as a result of decomposition of these functionalgroups upon pyrolysis.

The as-synthesized polymers may be used to prepare slurries usingsilicon and the as-synthesized polymers as the binder, followed bydoctor blade coating to prepare silicon-dominant anodes. The activematerial may be pyrolyzed under an argon atmosphere (or any inertatmosphere) to generate silicon-dominant anodes of 50% or greatersilicon by weight. In accordance with the disclosure, “active material”may comprise the active material alone, or may encompass an entireelectrode coating layer, which includes the active material and othercomponents. The pyrolyzed anodes may show improved adhesion to coppercurrent collectors and desirable flexibility. The resulting anodes maybe capable of fast charging and show similar or better cyclingperformance compared to the current anode technology, which uses organicsolvents and lamination to a current collector for anode manufacturing.

The water soluble PAA-based polymer blends used as binders describedherein have one or more of the following advantages:

-   -   1) Environmentally friendly precursors for Si anode production    -   2) Faster and cost-effective anode fabrication    -   3) Increased cycle life of Si based Li ion batteries    -   4) Improved anode adhesion    -   5) Large-scale roll-to-roll anode manufacturability    -   6) Increased energy density.

In an example embodiment of the disclosure, a method and system aredescribed for water soluble PAA-based polymer blends (such asphenolic-PAA) for use as binders in silicon-dominant anodes. The watersoluble PAA-based polymer blend can be present in a slurry and used tocreate an electrode coating layer, which may be pyrolyzed. For example,in one embodiment, the battery electrode may comprise an electrodecoating layer on a current collector, where the electrode coating layeris formed from silicon and a pyrolyzed water-based phenolic-PAA polymerbinder. The water soluble PAA-based polymer blend (such as phenolic-PAA)may be crosslinked and/or further reacted. The electrode coating layermay comprise conductive additives. The current collector may compriseone or more of a copper, tungsten, stainless steel, and nickel foil inelectrical contact with the electrode coating layer. The electrodecoating layer may comprise more than 70% silicon. The electrode may bein electrical and physical contact with an electrolyte, where theelectrolyte includes a liquid, solid, or gel. The battery electrode maybe in a lithium ion battery. These binder systems can be used with othertype of electrochemical storage devices, including, but not limited to,Li—S (lithium sulfur), Na-ion (sodium ion), and/or Li-air (lithium-air).

As utilized herein, “and/or” means any one or more of the items in thelist joined by “and/or”. As an example, “x and/or y” means any elementof the three-element set {(x), (y), (x, y)}. In other words, “x and/ory” means “one or both of x and y”. As another example, “x, y, and/or z”means any element of the seven-element set {(x), (y), (z), (x, y), (x,z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means “one ormore of x, y and z”. As utilized herein, the term “exemplary” meansserving as a non-limiting example, instance, or illustration. Asutilized herein, the terms “e.g.,” and “for example” set off lists ofone or more non-limiting examples, instances, or illustrations. Asutilized herein, a battery, circuitry or a device is “operable” toperform a function whenever the battery, circuitry or device comprisesthe necessary hardware and code (if any is necessary) or other elementsto perform the function, regardless of whether performance of thefunction is disabled or not enabled (e.g., by a user-configurablesetting, factory trim, configuration, etc.).

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

1. A battery electrode, the electrode comprising: an electrode coatinglayer on a current collector, the electrode coating layer formed from anelectrode slurry comprising silicon and a water soluble PAA-basedpolymer blend, wherein said water soluble PAA-based polymer blendcomprises PAA and one or more additional water-soluble polymercomponents; wherein said one or more additional water-soluble polymercomponents comprises a polymer containing one or more functional groupsselected from the group consisting of —OH, NH—, NH2, and —COOH; andwherein said electrode slurry has a slurry viscosity of 1500-2000 cps.2. The electrode according to claim 1, wherein one of said one or moreadditional water-soluble polymer components is phenolic resin.
 3. Theelectrode according to claim 2, wherein the concentration of saidphenolic resin in the water soluble PAA-based polymer blend is <30 wt. %4. The electrode according to claim 1, wherein said water solublePAA-based polymer blend is a tertiary system comprising PAA and twoadditional water-soluble polymer components.
 5. The electrode accordingto claim 4, wherein said water soluble PAA-based polymer blend is atertiary system comprising PAA, phenolic resin and a third water-solublepolymer component.
 6. The electrode according to claim 1, wherein theelectrode coating layer further comprises conductive additives.
 7. Theelectrode according to claim 1, wherein the current collector comprisesone or more of a copper, tungsten, stainless steel, and nickel foil inelectrical contact with the electrode coating layer.
 8. The electrodeaccording to claim 1, wherein the electrode coating layer comprises morethan 70% silicon.
 9. The electrode according to claim 1, wherein theelectrode is in electrical and physical contact with an electrolyte, theelectrolyte comprising a liquid, solid, or gel.
 10. The electrodeaccording to claim 1, wherein the battery electrode is in a lithium ionbattery.
 11. A method of forming an electrode, the method comprising:creating an electrode coating layer from an electrode slurry comprisingan aqueous solution of a water soluble PAA-based polymer blend and Sipowder; fabricating a battery electrode by coating the slurry on acurrent collector; and pyrolyzing said electrode coating layer; whereinsaid water soluble PAA-based polymer blend comprises PAA and one or moreadditional water-soluble polymer components; wherein said one or moreadditional water-soluble polymer components comprises a polymercontaining one or more functional groups selected from the groupconsisting of —OH, NH—, NH2, and —COOH; and wherein said electrodeslurry has a slurry viscosity of 1500-2000 cps.
 12. The method of claim11, wherein one of said one or more additional water-soluble polymercomponents is phenolic resin.
 13. The method of claim 12, wherein theconcentration of said phenolic resin in the water soluble PAA-basedpolymer blend is <30 wt. %
 14. The method of claim 11, wherein saidwater soluble PAA-based polymer blend is a tertiary system comprisingPAA and two additional water-soluble polymer components.
 15. The methodof claim 14, wherein said water soluble PAA-based polymer blend is atertiary system comprising PAA, phenolic resin and a third water-solublepolymer component.
 16. The method according to claim 11, wherein theelectrode coating layer further comprises conductive additives.
 17. Themethod according to claim 11, wherein the current collector comprisesone or more of a copper, tungsten, stainless steel, and nickel foil inelectrical contact with the electrode coating layer.
 18. The methodaccording to claim 11, wherein the electrode coating layer comprisesmore than 70% silicon.
 19. The method according to claim 11, wherein theelectrode is in electrical and physical contact with an electrolyte, theelectrolyte comprising a liquid, solid, or gel.
 20. A battery, thebattery comprising: a cathode, a separator, an electrolyte, and ananode, the anode comprising an electrode coating layer on a currentcollector, the electrode coating layer formed from an electrode slurrycomprising silicon and a pyrolyzed water soluble PAA-based polymerblend, wherein said water soluble PAA-based polymer blend comprises PAAand one or more one or more additional water-soluble polymer components;wherein said one or more additional water-soluble polymer componentscomprises a polymer containing one or more functional groups selectedfrom the group consisting of —OH, NH—, NH2, and —COOH; and wherein saidelectrode slurry has a slurry viscosity of 1500-2000 cps.
 21. Thebattery of claim 20, wherein one of said one or more additionalwater-soluble polymer components is phenolic resin.
 22. The battery ofclaim 21, wherein said water soluble PAA-based polymer blend is atertiary system comprising PAA and two additional water-soluble polymercomponents.
 23. The battery of claim 22, wherein said water solublePAA-based polymer blend is a tertiary system comprising PAA, phenolicresin and a third water-soluble polymer component.